Conventionally, a rotational speed detecting sensor for detecting a vehicle speed, or the like, includes a detecting member, which is housed in a case made of resin, or the like, and fixed at a vehicle side by means of a fix portion. The detecting member is provided facing a portion to be detected, which is attached to an object to be detected such as an inner race of a bearing, or the like, and integrally rotatable with the object to be detected. The detecting member detects a rotational speed of a rotor by detecting amount of a magnetic flux, which is varied in response to a rotation of a magnetized portion to be detected. Therefore, with the configuration of such rotational speed detecting sensor, the detecting member might necessarily be positioned reliably within a guaranteed magnetic flux area, which is generated by means of the portion to be detected.
A known rotational speed detecting sensor configured as described above is disclosed in JP2003-014498A. The disclosed rotational speed detecting sensor includes a detecting portion, a case, and a fix portion. After the detecting portion is reliably fixed to the case, the case is formed with the fix portion for fixing the detecting portion to the vehicle by means of resin molding. Therefore, the detecting portion can be disposed in the vicinity of the portion to be detected without difficulty.
However, because the disclosed rotational speed detecting sensor forms the fix portion relative to the case, a positioning of the detecting member relative to the fix portion might be difficult. Further, a position of the case housed in a mold may occasionally be shifted caused by, for example, the resin supplied into the mold at the time of forming the fix portion, or a handling of a work at the time of a setting of the mold. Therefore, a positional relation of the fix portion and the detecting member might be unreliable, and even when the fix portion is reliably fixed to a vehicle body at a predetermined position, a relative position of the portion to be detected and the detecting member may occasionally be shifted. More particularly, the positioning of the detecting member of the disclosed rotational speed detecting sensor might be unreliable in a direction in which the rotational speed detecting sensor is protruded from the fix portion as a base member, (a radial direction of the rotor to which the portion to be detected is attached) and an optimal detecting sensitivity may on occasions fail to be obtained.
A need thus exists for a rotational speed detecting sensor which ensures a relative positioning of the detecting member and the portion to be detected in the radial direction of the rotor.